Processes for recovering oligomers of glycols and polymerization catalyst from waste streams

Abstract

Processes for recovering and recycling oligomers and polymerization catalyst from aqueous waste streams generated during the production of polyalkylene ether glycols are provided. The processes utilize membranes; preferably reverse osmosis or nanofilter membranes. The processes can reduce waste and costs associated with the polymerization of polyalkylene ether glycols by recovery and recycling of glycols and catalysts

Description

[0001] This application is a Continuation of U.S. patent application Ser. No. 10 / 423,363, filed Apr. 25, 2003, the entire disclosure of which is hereby incorporated by reference.FIELD OF THE INVENTION [0002] This invention relates to membrane processes for recovering and recycling oligomers and polymerization catalyst from waste streams generated during the production of polyalkylene ether glycols. BACKGROUND [0003] Polyalkylene ether glycols, including polyethylene glycol, poly(1,2-propylene ether) glycol, and polytetramethylene ether glycol, are widely used in industry for various end use applications. They are used widely as lubricants or as starting materials for preparing lubricants used in the molding of rubbers and in the treatment of fibers, ceramics and metals. They are also used as starting materials for preparing cosmetics and medicines, as starting materials or additives for water-based paints, paper coatings, adhesives, cellophane, printing inks, abrasives, and surfacta...

AI Technical Summary

Benefits of technology

[0009] In some preferred embodiments, the aqueous wash stream contains 1 to 20% by weight of the polyalkylene ether glycol oligomers and further comprises one or more polymerization catalysts contained in the retentate.

[0010] In one embodiment the membrane is a reverse osmosis membrane and has a sodium chloride rejection rate preferably at least about 95% and more preferably at least about 99% under standard conditions. Preferably, the aqueous wash stream is fed to the reverse osmosis membrane at a pressure of from about 50 to about 1,000 psi, more preferably from about 150 to about 600 psi.

[0011] In another embodiment the membrane is a nanofilter membrane and has a magnesium sulfate rejection rate preferably at least about 80%, more preferably at least about 95%, under standard conditions. Preferably, the aqueous wash stream is fed to the nanofilter membrane at a pressure of from about 50 to about 400 psi, more preferably from about 100 to about 200 psi.

[0012] In one embodiment the process comprises providing two or more membranes arranged in parallel or series.

[0013] Preferably the aqueous wash stream contains 1 to 20% by weight of the polyalkylene ether glycol oligomers and further comprises one or more polymerization catalysts that are contained in the retentate. More preferably the aqueous wash stream comprises one or more acids used as a polycondensation catalyst in the polycondensation reaction, and the acids are contained in the retentate. More preferably the aqueous wash stream comprises 0.1 to 2 wt. % acid.

[0014] In a preferred embodiment, the polyalkylene ether glycol is selected from the group consisting of polyethylene ether glycol, poly(1,2-propylene ether) glycol, polytrimethylene ether glycol and polytetramethylene ether glycol. More preferably the monomeric diol comprises 1,3-propanediol, the polyalkylene ether glycol is polytrimethylene glycol, and the aqueous wash stream comprises polytrimethylene ether glycol oligomers, preferably having a number average molecular weight less than about 500.

Problems solved by technology

Depending on the molecular weight of the polymer, a significant amount (typically in the range of 1-20% by weight) of low molecular weight fraction can be extracted out, resulting in reduced yields of polymer.

Washing is also capital intensive since it results in an aqueous stream that requires distillation of large amounts of water to recover the low molecular weight oligomers before discharge.

These conventional waste treatment processes can create high capital, maintenance, and operating costs.

However, such a membrane-based procedure is impractical for commercial use with the two-phase initial product described above.

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